Conventionally, there have been proposed various applicator products with application materials that are decolorized or change their color as soon as applied to an object. Here, “applicator product” refers to products for applying application materials, for example, glue, adhesive, colorant such as ink, oil and others, in general.
As one of the those corresponding to the applicator products described above, what is called a stick glue is cited (see Non-Patent Document 1, for example). In the stick glue, a sealed container contains a solid glue exhibiting alkalinity into which a pH indicator is mixed so that the solid glue is in colored state. After the solid glue in colored state is applied, the color of the pH indicator fades away by exposure to air, that is, the glue is decolorized. Such glues have not only an advantage that an area where the glue is not applied to is easily found out because an area where the glue is applied to is clearly visible for an user just after applying, but also another advantage that the area where the glue is applied to fades after that and becomes inconspicuous. These advantages are a big factor that such glues are used widely.
By the way, photochromic compounds that develop colors by irradiation of light with a specific wavelength and are decolorized by irradiation of light with another specific wavelength are known. Many of the photochromic compounds have such a characteristic that those are capable of being colored clearly by irradiation of ultraviolet light with a specific wavelength and become colorless by irradiation of visible light with a specific wavelength. And, writing implements such as marker pens using the photochromic compounds are known as an example of applicator products with using the photochromic compounds (see Patent Documents 1 and 2, for example).
Now, there have been proposed applicator products in which a container to contain an application material or a nozzle to apply the application material directly is transparent or translucent so that the application material is visible from outside when or just before applied, in order to apply more accurate amount of the application material to an object or apply the application material to more accurate place or area on the object (see Non-Patent Document 2, for example).
However, when the application materials with the photochromic compounds are used in such applicator products as described above, the application materials cannot maintain those colored state on a long-term basis and are gradually decolorized depending on environments where the applicator products are stored because the application materials lose those colors by irradiation of light under natural conditions.